The present invention relates generally to eccentric disk grinders. In particular, it relates to an eccentric disk grinder which has a multi-part housing with a motor which eccentrically drives a grinding disk via a shaft so that the grinding disk is rotatable relative to the shaft about an axis of an eccentric pin or an eccentric shaft.
One such eccentric disk grinder is disclosed for example in the German reference DE-OS 36 25 655. Its grinding disk is driven by a motor. The rotation of the motor is converted via an angular transmission on a shaft carrying an eccentric pin into the working movement which is composed of a rotary movement and a circular movement of the grinding disk. The shaft, supported at two points, carries at its free end a rotatable eccentric pin. The pin is rotatable with an eccentricity "e" relative to the shaft on which two ball bearings are arranged. The eccentric pin is coupled non-rotatably with the grinding disk and circulates together with it with the eccentricity "e" around the axis of the shaft and therefore rotates due to the bearing friction with the shaft.
The bearings between the eccentric shaft and the shaft are subjected to high, non-uniform loading. This leads to intense heat generation and wear, when not unconventionally intensive heat withdrawal is performed, for example by a cooling fan.
The cooling of the bearings in abrasive medium-containing air, typical of a grinding machine, requires especially expensive seals of the bearings which are simpler for ball bearings than for roller bearings. Due to the required good heat withdrawal, metal fans must be utilized which are heavier than synthetic plastic fans and need stronger bearings.
Some driven shafts of hand-held power tools which are vibration-technically simple and have low abrasive-dust loading, for example drilling machines and plunge saws, are supported in radial-axial bearing pairs and the radial bearings are arranged at the side facing the tool. This solution is, however, not transferable to the eccentric disk grinders. The bearing calculations for eccentric disk grinders due to the complicated superimposed movements and the imbalance involve only coarse approximation solutions. The actual bearing forces can be determined only by substantial experiments. Only in this way can the bearing arrangement be determined. Due to the unpredictable bearing computations, until the present time many over-dimensioned axial-radial ball bearings have been utilized, while roller bearings or needle bearings are substantially more price favorable than ball bearings. This makes the known devices significantly more expensive.